Printing cloth

ABSTRACT

A PRINTING CLOTH, ESPECIALLY FOR OFFSET PRINTING, WHICH INCLUDES: A BASE LAYER OF ELASTOMERIC MATERIAL HAVING A MAXIMUM THICKNESS OF 0.7 MM. AND COMPRISING AT LEAST ONE FABRIC PLY OF FIBER MATERIAL HAVING A HIGH MODULUS OF ELASTICITY, A VOLUME COMPRESSIBLE LAYER OF ELASTOMERIC MATERIAL HAVING A THICKNESS OF AT LEAST 0.6 MM. AND HAVING EMBEDDED THEREIN A HIGH PERCENTAGE OF CORK PARTICLES, AND A HIGHLY ELASTIC COVER LAYER OF AT LEAST ONE SOLVENT RESISTANT POLYMER AND HAVING A THICKNESS OF FROM 0.2 TO 0.5 MM., SAID BASE LAYER AND VOLUME COMPRESSIBLE LAYER AND COVER LAYER BEING PLACED UPON AND VULCANIZED TO EACH OTHER.

E. VOLMER PRINTING CLOTH July 11, 1972 2 Sheets-Sheet. l

Filed Maron zo, 1970 NN om mr f m mf mf N- D.. m

July l1, 1972 E.vo1.MER 3,676,232

PRINTING CLOTH Filed lax-oh 20, 1970 2 Sheets-Sheet a 1,0 l 9 f A I y 'l' ole G I 3 l /An 07 1a 2 3) v/ y ,/"r 5 0,4 f l L x lb 2 'la h INVENTOR Ward/2a ya /wp/ United States Patent O U.S. Cl. 161-87 2 Claims ABSTRACT OF THE DISCLOSURE A printing cloth, especially for offset printing, which includes: a base layer of elastomeric material having a maximum thickness of 0.7 mm. and comprising at least one fabric ply of fiber material having a high modulus of elasticity, a volume compressible layer of elastomeric material having a thickness of at least 0,6 mm. and having embedded therein a high percentage of cork particles, and a highly elastic cover layer of at least one solvent resistant polymer and having a thickness of from 0.2 to 0.5 mm., said base layer and volume compressible layer and cover layer being placed upon and vulcanized to each other.

The present invention relates to printing cloths, which have an expansion resistant carrier layer, a volume compressible layer and a cover layer. With offset printing, the cover layer of the printing cloth is intended for the dye transfer and with other printing methods takes care of the paper being uniformly pressed against the print carrier.

Printing cloths with a volume compressible intermediate layer are known per se and in this connection there exist two different types, namely printing cloths the microporosity of which consists of individual non-interconnected pores, and printing cloths the pores of which are interconnected by ne passages.

Under normal conditions of use, both types of printing cloths furnish satisfactory prints. If, however, it is desired to print upon products, such as envelopes, which have thickened portions, or if the feeding of the paper is disturbed in such a way that folded over or thickened corner portions are formed, the printing cloths of the first mentioned type will when relatively heavily thickened portions are involved be destroyed in a rather short time and will become non-usable, while the printing cloths with interconnected micropores do not recover fast enough and thus furnish faulty prints on the products which follow the respective disorder or disturbance. These cloths are, therefore, stopper proof or resistant to Stoppers only to a limited extent. This insufficient stopper resistance can be explained as being caused by a larger amount of air escaping from the micropores which are compressed to a greater extent in the region of the stopper, through the ne passages between the individual micropores. When the pressure is relieved, the escaped air volume is, therefore, no longer available for furnishing sufficiently high returning forces.

There have also become known volume compressible printing cloths which have'been accepted in newspaper printing as underlayer cloths only. These printing cloths have a kind of double porosity which is created by the fact that the micropores of printing cloths of the first mentioned type are filled with cork particles which in their turn have a porosity of their own. The pore volume is in this instance considerably reduced by the employed cork substance so that if such volume compressible layer is used in connection with offset printing cloths, a sufficient compressible total volume can no longer be obtained. It

3,676,282 Patented July 11, 1972 ICC is a well known fact that in offset printing machines only a limited space of from about 1.4 to 1.9 mm. is available for the layer thickness of the printing cloth.

Inasmuch as due to the requirements with regard to strength and little expandability in the pull carrier layer, according to the heretofore prevailing opinion, a certain thickness appeared to be necessary for the pull carrier layer, and since also a space must remain for the cover layer, it was impossible with printing cloths containing a volume compressible cork incorporating layer to realize the advantages of the volume compressibility to a satisfactory extent in View of the remaining small layer thickness.

In particular, when so-called Stoppers occur with this type of printing cloths, an even faster destruction of the compressible intermediate layer will result than was the case with printing cloths in which the microporous intermediate layer consists only of rubber.

It is, therefore, an object of the present invention to provide a printing cloth, especially for offset printing, which will overcome the above mentioned drawbacks.

It is another object of the present invention to provide a printing cloth as set forth in the preceding paragraph, which has an increased stopper resistance and excels by a longer life.

These and other objects and advantages of the invention will appear more clearly from the following specification in connection with the accompanying drawings, in which:

FIG. 1 is a cross-section through a printing cloth according to the invention.

FIG. 2 shows the spring characteristic of two printing cloths respectively containing and 70 percent per volume of cork in the volume compressible layer and indicates the extent of compression in response to a pressure exerted upon the surface unit.

FIGS. 3 and 4 respectively illustrate by way of a graph the values for the deformations remaining in the different types of printing cloths, curves 1a and 1b representing the printing cloths according to the invention, curve 2 representing a printing cloth with isolated micropores in the volume compressible layer, curve 3 representing a printing cloth with volume compressible layer having intercommunicating micropores.

The above outlined objects have been realized according to the present invention by a printing cloth which is characterized by the combination of the following features:

(a) The bottom layer consists of one or more plies of fabric material having a high modulus of elasticity, said bottom layer having a total thickness not exceeding 0.7 mm.

(b) The volume compressible layer comprises a rubber mixture with a high percentage of cork particles and has a thickness of at least 0.6 mm.

(c) The highly elastic and abrasion and solvent resistant cover layer has a thickness of from 0.2 to 0.5 mm.

Surprisingly, the volume compressible layer containing a high percentage of cork particles, when exceeding a certain layer thickness of approximately 0.6 mm., does not only have a considerably increased stopper resistance manifested by a high returning power, but simultaneously also possesses a considerably increased life, even when being subjected to extreme loads. This phenomenon can be explained theoretically only by assuming that the forces occurring during a printing operation in the volume compressible layer and causing a destruction are compensated for when exceeding a critical layer thickness and thus are no longer effective. This becomes apparent in the following comparison.

If with a printing cloth built up in the conventional manner, the volume compressible layer of which has a thickness of from 0.3 to 0.4 mm., cork particles are admixed in a proportion corresponding to the pore volume, there will be obtained a print of inferior quality, even though inferior to a very small degree, and a life span of the printing cloth which is reduced by half the usual life span. Apparently the cork particles have an abrasive effect on the surrounding rubber layers in case layer thicknesses as mentioned above are involved.

If, however, the thickness of the intermediate layer is, at the expense of the strength of the bottom layer consisting of fabric, increased to values exceeding 0.65 mm., preferably to a value of about 1 mm., in addition to an increased life span of the volume compressible layer, there is simultaneously also obtained an improvement in the printed picture, in other words in the stopper resistance. These effects occur even when the proportion of cork particles is still further increased and are particularly satisfactory even with such a high proportion of cock particles that it is just barely possible properly to intermix the cork particles with the rubber mixture.

The seemingly resulting drawback of weakening the bottom layer can be compensated for by the employment f fabrics having a high tear resistance and a low expansion, which fabrics consist of so-called modal fibers, i.e. fibers having a particularly high modulus of elasticity. Such fibers, preferably of regenerative cellulose, have been known for some time and, therefore, do not represent a part of the present invention. The employment of such fibers for the manufacture of fabrics makes possible the employment of thin fabric layers in printing cloths, which fabric layers at the same time have the advantage of a low expansion in the direction of the wefts and warps.

By the favorable combination accordinng to the invention of the above mentioned features of the volume compressible layer and the bottom layer, a printing cloth is obtained which has high recovery powers, i.e. a high stopper resistance and a surprisingly long life span. The proportion of the cork particles in the volume compressible layer amounts preferably to from 70-180 percent by volume with respect to the rubber mixture. With a proportion of cork particles of less than 70 percent by volume, already a decrease in the recovery forces is noticeable, the upper limit being determined by the extent to which the cork particles can be mixed with the rubber mixture. The proportion of cork particles could still be increased, for instance, when employing rubber mixtures of low viscosity. However, experience has taught that in such an instance other undesirable properties will occur which means that the limit of 180 percent by volume of cork particles which can still be mixed with the rubber mixture, is to be considered the upper limit.

As basic polymer for the manufacture of the rubber mixture receiving the cork particles, preferably synthetic rubbers may be employed which are resistant to solvents and oil, for instance, butadiene nitrile mixed polymerisates.

The highly elastic cover layer likewise consists of polymers resistant to oil and solvents and may be kept within4 conventional limits with respect to the structure of the mixture and of the thickness of the layer.

The cover layer may, as is well known, be provided with a rough surface by embedding therein glass or quartz splinters or pellets.

Referring now to the drawings in detail and FIG. 1 thereof in particular, the printing cloth shown therein comprises a rubber layer 3 which is resistant to solvents, and fabric layers 1 and 2. The fabric layers 1 and 2 which are connected to each other by the rubber layer 3 form the bottom layer which in the particular example has an overall thickness of 0.6 mm. The fabric layer is built up of thin fibers having a high modulus of elasticity, said fibers consisting of regenerated cellulose.

The volume compressible intermediate layer 4 consists of a rubber mixture which is non-sensitive to oils and solvents on the basis of butadiene acrylic nitrile mixed polymerisates into which has been mixed in the specific example percent by volume of finely :ground cork particles. The volume compressible layer has been deposited upon the bottom layer in a thickness of 0.9 mm. and has been covered by an oil and solvent resistant cover plate 6 having a thickness of 0.3 mm.

After the layers had been interconnected, the entire body was vulcanized.

For purposes of comparison, a further printing cloth of the same structure was built up which, however, contained only 70 volume percent of cork particles in the volume compressible layer.

The spring characteristics of these two printing cloths are shown in FIG. 2. The spring characteristics show the compressibility per surface unit when the cloth is subjected to a certain pressure. The spring characteristic of the first printing cloth is represented by the curve 1a whereas the spring characteristic of the second printing cloth is represehted by the curve 1b. While in the case 1a a linear volume compressibility has been obtained, this holds no longer true in case 1b over a wide range.

In order to permit a comparison of the printing cloths according to the present invention with the printing cloths of the prior art with respect to the returning forces after the cloths have been subjected to a static and a dynamic load, FIGS. 3 and 4 give the values for the remaining deformations in the printing cloths 1a and 1b, for a printing cloth with a volume compressible layer 2 having isolated micropores, and for a printing cloth 3 with a volume compressible layer having intercommunicating micropores. FIG. 3 shows the values for the static deformation. In a pinch-hardness-testing device there was measured the deformation which remained after one second and which was obtained by pressing a ball having a diameter of l0 mm. for two seconds against the printing cloth to obtain a certain starting deformation thereof. For the printing cloths 1a and 1b, no deviations showed within the limit of the measuring errors so that a showing of a second curve was not necessary. The air filled printing cloth 2 having insulated micropores showed within the limits of the measuring errors approximately the same course, 'whereas the printing cloth 3 with the interconnected micropores clearly showed a decrease in the returning forces as reflected by a considerable remaining deformation.

While the remaining deformation, expressed in percent, varies with the printing cloths 1 and 2 from 22 to 25%, this percentage varies with the printing cloth 3 from 35 to 40%.

FIG. 4 illustrates the remaining deformation as a function of the recovery period after being subjected to a dynamic load of 300,000 strokes in 18 hours with a compression of Ifrom 0.3 mm.i0.03 mm. per stroke with a punch of 1 om?. Such load occurs in practice, for instance, when printing upon prefabricated envelopes. In this connection it has been found that the printing ycloth 3 after such load shows a remaining deformation of 0.15 mm. on the respective areas subjected to the load, which deformation after a recovery period of three hours decrease only to about half. Such a high remaining deformation does no longer assure a uniform clear print.

In contrast thereto, the printing cloths 1a and 1b, 2 after having been subjected to the same load show a considerably lower remaining deformation. The printing cloth 1a retains a trace of an impression of 0.04 mm., which is hardly visible with the naked eye and which after a certain time is reduced to half, i.e. to 0.02 mm. Also the originally present impression of 0.08 mm. in the printing cloth 1b recovers very rapidly and already after two hours is reduced to the value of 0.02 mm., i.e. the value obtained with the printing cloth 1a.

The printing cloths 1a and 1b correspond as to their properties during the printing operation substantially to those of the printing cloth 2, whereas they are far superior to the printing cloth 3. Surprisingly it has been found that the life expectancy of the printing cloths 1a and 1b on the printing machines is about t-wice that of the printing cloths 2 and 3. In this connection it is to be understood that the printing cloth -3 will become nonusable due to the remaining deformations at a much faster rate although its structure has not yet been attacked.

It is, of course, to be understood that the present. invention is, by no means, limited to the particular structure shown in the drawings but also comprises any modifications within the scope of the appended claims.

What I claim is:

l. A printing cloth, especially for oiset printing, which consists of: a base layer of elastomeric carrier material having a maximum thickness of 0.7 mm. and comprising at least one fabric ply of liber material having a high modulus of elasticity, an intermediate volume compressible layer of elastomeric rubbery material having a thickness of at least 0.6 mm. and having embedded therein 70-180 percent by volume of cork particles, with regard to the rubbery material and a highly elastic cover layer of at least one solvent resistant polymer and having a thickness of from 0.2 to 0.5 mm., said base layer and said inter- References Cited UNITED STATES PATENTS 1,158,033 10/1915 Ellis 161--87 2,792,322 5/1957 Fredericks 161--401 2,104,692 1/ 1938 Cooke et al 260--37 R 2,207,999 7/ 1940 Foster 161-211 3,012,498 12/1961 Gurin 161--401 3,235,772 2/ 1966 Gurin 161-401 ROBERT F. BURNETT, Primary Examiner L. C. KOECKERT, Assistant Examiner U.S. Cl. X.R. 

